1892.] Physiology. 1053 
amount of the ganglion present, until motion may be caused by stimuli 
so slight or of such a nature that they are not apparent. 
The objection to which all experiments of this nature are more or 
less open may be raised here: viz, that the mutilation which is un- 
avoidable in the operation would cause weakness and perhaps an 
apparent loss of function, even if no absolutely essential portions of the 
nervous system were removed. However, where the superæsophageal 
ganglion is not involved, the animal endures mutilation to such an 
extent without losing its volition and activity that the influence 
of the ganglion must be real and not apparent. Moreover, there is 
another fact which proves that the ganglion exercises a real influence. 
This fact is the presence of the so-called “ forced motions” after an 
asymmetrical operation upon the ganglion. In all such cases the 
animal turns toward the uninjured side as it crawls, and thus goes 
about in a circle. This circular forced motion can be induced by a 
burn upon one side of the ganglion, and also by removal of one-half 
of the head with a pair of fine, sharp scissors. The animal recovers 
from the latter operation, and sometimes lives for twenty-four hours. 
The degree in which the forced motion is evident varies considerably. 
In some cases the diameter of the circle in which the animal moves is 
not more than an inch, while in other cases it is six or eight inches. 
The tendency to move in a circle appears to increase in strength as 
the animal becomes weaker, until sometimes, when nearly dead, it lies 
upon one side and turns within its own length. Two cases were 
observed in which the animal turned toward the injured side. In both 
these the operation was a burn on one side of the supercesophageal 
ganglion. Owing to accident the observations in both cases were not 
continued beyond the first so that the later phenomena are not known, 
but it seems probable that these forced motions resulted from irritation 
in the wound. A number of attempts were made in large specimens 
to cut one of the cesophageal commissures, but, owing to the extremely 
small cesophageal opening, and the small size of the animal, they were 
not successful. Steiner in a short article published a year or two since 
(Die Funktionen des Centralnervensystems der wirbellosen Thiere), 
states that with his large Tulidae he was able to cut a single com- 
missure, and obtained very evident circular forced motion toward the 
uninjured side. 
The supercesophageal ganglion, then, is a motor center to which all 
the motor centers lying in the ventral cord are subordinated. It 
enables them to respond to sensory stimuli with greater exactness and 
strength than would otherwise be possible. Besides this it is evidently 
